Patent No. FR-A-2625711 describes an active hydropneumatic suspension for automotive vehicles, comprising an hydraulic jack linked to each of the wheels and equipped with a main chamber connected by means of a shock absorber to a main hydropneumatic accumulator, as well as three height regulators, which are linked respectively to each of the front jacks and to the two jacks on the rear axle. Each regulator is connected, first, to a pressurized fluid source by means of a compensating hydropneumatic accumulator and to an outflow tank or reservoir, and, secondly, to the main chamber(s) of the associated jack or jacks.
These height regulators are actuators, such as hydraulic slide valves or solenoid valves, capable of sending fluid into a line incorporating the main chamber of the associated jack, or of removing liquid therefrom so as to correct for height variations of the vehicle body. This arrangement provides a suspension which not only reacts conventionally to normal road irregularities, but can also compensate for vertical spring movement of the suspension components when the latter undergo expansion or compression stress for a long period, with the result that the vehicle preserves stability and position-retention in relation to the average ground contour, in particular during rolling when turning or pitching when accelerating and braking.
Spring movement of the body is corrected by taking into account body height and various parameters representative of the dynamic state of the vehicle. However, this motion is controlled hydromechanically. Correction always occurs at the same rate, and, depending on the case, it may occur too slowly or too rapidly to ensure proper vehicle stability.